In known manner, for calibrating ionizing radiation detectors of a nuclear medicine apparatus, use is made of a liquid radioactive source maintained in a container. This container is placed in the detection zone of the detectors prior to each observation of a patient.
FIG. 1 diagrammatically shows a nuclear medicine apparatus 2, within which is placed a known type of container 6, containing a liquid radioactive source 1. The apparatus 2 comprises a group of detectors 4 e.g., placed in the case of a tomography apparatus in such a way as to form a cylinder or a portion of a cylinder. The inner zone of the cylinder corresponds to the detection zone 8 of the apparatus 2.
The group of detectors 4 is generally mobile, so that it is possible to observe the patient in all directions in space, when he is placed in the centre of the detection zone 8.
The container 6 has a shape adapted to the group of detectors 4. It is therefore cylindrical in the case of a tomography apparatus, and its length generally exceeds that of the latter.
As shown in FIG. 1, the container 6 is formed by an annular chamber containing the liquid radioactive source 1, or by a winding of turns filled with the source 1.
During a calibration operation, the container 6 is placed in the detection zone 8 so that it is centered with respect to the group of detectors 4.
Following each calibration, the container 6 is removed from the detection zone 8, so as not to disturb the measurements performed on a patient placed in the centre of the detection zone. The container 6 is then placed in a shielded enclosure 10, which is generally made from lead in order to protect the environment from ionizing radiation emitted by the source 1 in the container 6.
In known manner, the container 6 is alternately placed in the detection zone 8 and in the enclosure 10, either manually by an operator or by automatically controlled displacement means (not shown).
The manual method of introducing the container 6 into the detection zone 8 and its arrangement in the enclosure 10 makes it possible not to overburden the detection zone with control means. However, this method does not protect personnel from ionizing radiation.
The automatic control method makes it necessary to at least partly place the enclosure 10 in the detection zone 8. Automatic displacement controls then make it possible to place the container 6 either in the centre of the detection zone 8, or in the enclosure 10. Thus, this method makes it possible to avoid exposure of personnel, but makes it necessary to place the automatic displacement control means and the enclosure at least partly in the detection zone, which greatly overburdens the latter.